Abstract 11438: Thyroid Hormones and Changes in Body Weight and Metabolic Parameters in Response to Weight-Loss Diets: The POUNDS LOST Trial

Context: The role of thyroid hormones in diet-induced weight loss and subsequent weight regain is largely unknown. Objective: To examine the relationship between baseline thyroid hormones and subsequent changes in body weight and resting metabolic rate (RMR) in a diet-induced weight-loss setting. Methods: In the 2-year POUNDS LOST randomized clinical trial that tested 4 weight-loss diets, thyroid hormones (free triiodothyronine [T3], free thyroxine [T4], total T3, total T4, and thyroid stimulating hormone [TSH]), and resting metabolic rate (RMR), as well as anthropometric and biochemical parameters, were determined at baseline, 6 months, and 2 years among 569 overweight and obese participants aged 30-70 years with normal thyroid function. Results: Participants lost an average of 6.6 kg of body weight during the first 6 months and subsequently regained an average of 2.7 kg of body weight over the remaining period from 6-24 months. Baseline free T3 and total T3 levels were positively associated with baseline body mass index and RMR, whereas free T4, total T4, and TSH did not demonstrate a clear pattern of correlations with these parameters. After multivariate adjustment including dietary intervention groups and baseline body weight, higher baseline free T3 and free T4 levels were significantly associated with a greater decrease in body weight in the first 6 months. Comparing extreme tertiles, the weight loss was -5.39±0.9 vs -3.87±0.9 for free T3 (P trend=0.02) and -5.88±0.9 vs -4.09±0.9 for free T4 (P trend=0.004). The thyroid hormones did not predict weight regain between 6 and 24 months. The associations were attenuated after further adjusting for changes in RMR. Conclusion: In this diet-induced weight-loss setting, higher baseline free T3 and free T4 predict more weight loss, but not weight regain among overweight and obese adults with normal thyroid function. In addition, changes in RMR may partially mediate the observed associations. These findings reveal a novel role of thyroid hormones in body weight regulations and may help identify individuals more responsive to weight-loss diets.